Given the task definition and input, reply with output. You are given a passage. You need to construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) its answer is the whole paragraph. Avoid creating questions that can be answered correctly without actually understanding the paragraph.

This is pretty much a question of the definition you are using.\n\nIn a strict definition, conventional solids have a crystalline structure. Under this definition, glass is a supercooled, highly viscous liquid rather than a conventional (crystalline) solid. \n\nIn many ways, glass acts like a solid. Using that behaviour as a criterion, glass is a solid.

Over hundreds of years, the glass in glass windows sinks down to the bottem.  So is glass a liquid or a solid?